Polyrotaxanes Glass temperature

Gibson et al. [109] and Sjen et al. [110] reported pseudo-polyrotaxanes and polyrotaxanes consisting of crown ethers with various polymers. The resulting polyrotaxanes were nonstoichiometric. Their properties - including solubility and glass transition temperatures - were different from those of the starting polymers. 

A glass transition temperature (Tg) is the temperature at which polymer is transformed from the glassy state to a rubbery state. The T values observed for polyrotaxanes might differ from the starting backbone if only one phase is formed, i.e., when the cyclic is compatible with the backbone. If the cyclic is immiscible with the backbone, two phases corresponding to two components might be formed. For these polyrotaxanes, two Te values might be observed if both components are amorphous. 

Because of their novel topologies, polyrotaxanes have properties different from those of conventional polymers. Solubility, intrinsic viscosity, melt viscosity, glass transition, melting temperature and phase behavior can be altered by the formation of polyrotaxanes. The detailed changes are related both to the properties of the threaded cyclics and to the backbone and the threading efficiency. 

Polyrotaxanes have been prepared by threading multiple a-cyclodextrin units onto a bulky benzimidazole-based linear chain polymer with an aliphatic spacer where the cyclodextrin resides. The rotaxane forms as the cyclodextrin-bound precursor amine is polymerised. Compared to the polymer in the absence of the cyclodextrins, the glass transition temperature is raised by some 20 °C even though only ca. 16 % of the aliphatic spacers in the polymer are rotaxanated.28 A novel approach to polyrotaxanes involved the use of a metal ion such as Zn2+ to thread a phenanthroline-based macrocycle onto a thiophene-based complementary monomer. The resulting pseudorotaxane can then be electropolymerised and the Zn2+ ions removed to give a polyrotaxane, Scheme 14.5. The redox and conductivity properties of the polymer are very much dependent on whether a metal ion is bound or not.29... 

Ritter et al. [147-155] have been studying side chain poiyrotaxanes. They synthesized side chain poiyrotaxanes by amide coupling of polymer-carrying carboxylic acid moieties with various semirotaxanes of methylated /l-CD(s) and an axle bearing an amine group at one end [147-154]. These works have been reviewed in an excellent review by Raymo and Stoddard [78]. Ritter et al. [155] reported recently a new type of side chain polyrotaxane. They polymerized inclusion complexes of di(meth)acrylates of butan-l,4-diol and hexan-l,6-diol with a-CD and with methylated /1-CD using a redox initiator system in aqueous media, and characterized the polyrotaxane structure by IR and glass-transition temperature measurements. 

A noteworthy feature of the polyurethanes of Table 43.1 is that the model polymer, the first entry, is insoluble in water, dichloromethane and acetone, whereas both the polyrotaxanes derived from 36-crown-12 and 60-crown-20 , la and Id, respectively, are soluble in these three solvents [32]. The glass transition temperatures of the polyurethane rotaxanes of Table 43.1 obey the Fox equation (see Fig. 43.1) this is due to... 

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